It is known that the substances or products which are intended to be freeze-dried, such as foodstuffs or pharmaceuticals, prior to being subjected to the freeze-drying process proper in evacuated cells, should be properly metered and pre-frozen. These two metering and pre-freezing stages have been carried out heretofore in a batchwise run, in different apparatus with the result being a considerable waste of time, especially when multi-layered products are to be pre-frozen, inasmuch as the metering and pre-freezing steps should be repeated for each layer of the product.